This invention relates to steerable antennas, and more specifically relates to the rejection of interfering signals in such antennas.
In communications systems, there is a need to protect some critical receive functions (such as GPS) against one or more external interfering sources by employing the use of steerable null antennas having multiple antenna elements. Because space on aircraft, (especially on military fighters) is very limited, the number of antenna elements must be kept to an absolute minimum. The number of interferers that can be nulled by such a multi-element antenna is limited by the number of it""s steerable elements. Since multiple interferers can exist, it is possible that the number of interferers can exceed the antenna element count, and thus compromise the ability of the antenna to cancel. This invention addresses this problem and provides a solution.
The invention is useful in a steerable antenna comprising a plurality of antenna elements receiving a first type signal and an interfering second type signal different from the first type signal. The antenna elements generate corresponding antenna signals, and the antenna signals are combined with weighting signals to form at least one combined signal. In such an environment the interfering second type signals may be nulled by filtering the second type signal from the combined signal to generate a filtered signal. The filtering preferably is accomplished with a processor. The weighting signals are generated in response to the filtered signal and the antenna signals. The generating of the weighting signals also is preferably accomplished with a processor. As a result, interference from the second type signal is reduced.